At the end of the day, though, it’s functionally largely equivalent to a moderated comment system, which has existed for a while. The difference to date has been the way responses are presented and framed. Calling it a “response” rather than a “comment” raises the perceived quality bar, at least for some users. The general elegance of Medium (the lingering but deteriorating perception that it’s for well-written, long-form writing) also makes it less likely that people will leave YouTube-style comments.

However, the more that the user interface is tuned to promote responding — making it feel easier and more casual so more people do it — the more that responses will come to resemble traditional moderated comments. I think there’s a simple one-dimensional spectrum here, from intimidating/high perceived quality bar/not much garbage, at the one extreme, to really easy/low bar/lots of garbage, at the other, and Medium can decide where it wants to be on that spectrum. I don’t think there’s a way to create a system that lots of people will participate in and that doesn’t generate lots of garbage (which I will have to wade through in order to find the responses that I want to recommend). But maybe there is and maybe Medium will figure it out.